Beacon and associated components for a ranging system

ABSTRACT

A beacon for a ranging system includes an electronic scanned array (ESA) antenna and a transceiver. The ESA antenna is configured to emit a separate radio frequency (RF) phased-array narrow beam for each of a plurality of segments of an arc, and receive from an end user node a response signal based on at least one of the RF phased-array narrow beam. Each segment of the arc is scanned at a specified time interval. The transceiver is configured to transmit a pulsed signal via the RF phased-array narrow beam, and receive the response signal.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 13/430,525, filed Mar. 26, 2012 which is a continuation of PCTInternational Application No. PCT/US12/26666, filed Feb. 24, 2012 whichclaims the benefit of U.S. Provisional Patent Application Ser. No.61/446,470, filed Feb. 24, 2011, and U.S. Provisional Patent ApplicationSer. No. 61/446,474, filed Feb. 24, 2011, each of which is incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates generally to terrestrial positioning andranging. Accordingly, the present invention involves the fields of radiofrequency based perimeter positioning and ranging and messaging.

BACKGROUND

Satellite navigation systems, such as the global positioning system(GPS) available to military, civil, commercial, and scientific users,enable a receiver to determine a location from ranging signals receivedfrom a plurality of satellites. GPS positioning and other locationservices within buildings can be unreliable or unavailable.Particularly, GPS positioning and other location services may beunreliable or unavailable inside buildings and structures, includinglarge industrial buildings, buildings with rooms, buildings withmultiple floors, or outdoors in areas, such as areas with thickundergrowth or other obstructions. Various technologies are used toimprove ranging technologies. Some ranging technologies involveestablishing a network of positioning stations throughout a structurewhich can then communicate with a satellite signal. However, such anapproach typically requires a pre-existing installation within thebuilding or structure. Furthermore, available technologies havesignificant limitations in terms of resolution and reliability in avariety of environments.

SUMMARY OF THE INVENTION

A beacon for a terrestrial ranging system includes an electronic scannedarray (ESA) antenna and a transceiver. The ESA antenna is configured toemit a separate radio frequency (RF) phased-array narrow beam for eachof a plurality of segments of an arc, and receive from an end user nodea response signal based on at least one of the RF phased-array narrowbeam. Each segment of the arc is scanned at a specified time interval.The response signal can include at least one of a transponder signal, atransceiver signal, or a repeat of either. The beacon is configured totransmit a pulsed signal via the RF phased-array narrow beam, andreceive the ‘end user node’ response signal. The response signal cancome from a transceiver or a transponder or a repeater. A transpondedsignal can be a frequency shifted copy of an original signal transpondedfrom a different location. A repeated signal can be a copy of theoriginal signal repeated from the different location. In an example, theranging system can include a processing module. The processing modulecan be configured to calculate at least one of an angle-of-arrival (AOA)and a time-of-flight (TOF) from the response signal and generate alocation of the end user node relative to a location of the beacon.

In another example, this technology can be used for emitting a radiofrequency (RF) phased-array narrow beam using a beacon. One method caninclude the beacon receiving an RF signal at a splitter and summermodule. The splitter and summer module can transmit the RF signal to aplurality of phase shifters. Each phase shifter can correspond to aradiator aperture in an electronic scanned array (ESA) antenna. Thephase shifter can phase shift each RF signal to form a narrow in-phasebeam in a specified direction. A plurality of radiator apertures canemit the phase shifted signals in a pattern of raster scans. The rasterscan can vary between a broad scan and a narrow scan based onprogramming of corresponding beamformers. The beacon can receive aresponse signal from an end user node at the plurality of radiatorapertures. The response signal can be received through an obstruction.

In another example, this technology can be used for communicatingbetween an end user node and a control station controller used indetermining a location of the end user node relative to a beacon. Onemethod can include the controller transmitting an inquiry message to theend user node with a minimum received signal strength indicator (RSSI)message. The minimum RSSI message can include a RSSI threshold fortransmitting a reply message from the end user node. The controller canreceive a reply message from the end user node including a measured RSSIof the inquiry message at the end user node when the measured RSSI ofthe inquiry message exceeds the RSSI threshold.

In another example, a control station controller for a ranging systemcan include a transmitting module and a receiving module. Thetransmitting module can be configured to transmit an inquiry message tothe end user node with minimum received signal strength indicator (RSSI)message. The minimum RSSI message can include a RSSI threshold fortransmitting a reply message from the end user node. The receivingmodule can be configured to receive a reply message from the end usernode including a measured RSSI of the inquiry message at the end usernode when the measured RSSI of the inquiry message exceeds the RSSIthreshold.

In another example, this technology can be used for communicatingbetween an end user node and a control station controller used indetermining a location of the end user node relative to a beacon. Onemethod can include the end user node receiving an inquiry message fromthe controller with minimum received signal strength indicator (RSSI)message. The minimum RSSI message can include a RSSI threshold fortransmitting a reply message from the end user node. The end user nodecan measure a RSSI of the inquiry message. The end user node cantransmit a reply message to the controller including the measured RSSIof the inquiry message at the end user node when the measured RSSI ofthe inquiry message exceeds the RSSI threshold.

In another example, an end user node for a ranging system can include areceiving module, a measurement module, and a transmitting module. Thereceiving module can be configured to receive an inquiry message from acontroller with minimum received signal strength indicator (RSSI)message. The minimum RSSI message can include a RSSI threshold fortransmitting a reply message. The measurement module can be configuredto measure a RSSI of the inquiry message. The transmitting moduleconfigured to transmit a reply message to the controller including themeasured RSSI of the inquiry message at the end user node when themeasured RSSI of the inquiry message exceeds the RSSI threshold

A ranging system includes at least one beacon and a control module. Theat least one beacon is configured to scan each segment in a plurality ofsegments of an arc with a narrow radio frequency (RF) beam and receive aresponse signal from an end user node in at least one segment. Eachsegment of the arc is scanned at a specified time interval. The controlmodule is configured to communicate with the at least one beacon. Thecontrol module is further configured to calculate at least one of anangle-of-arrival (AOA) and a time-of-flight (TOF) of a response signalfrom the end user node to the beacon and generate an end user nodelocation relative to a beacon location. In an example, the rangingsystem can include the end user node configured to receive at least oneof the narrow radio frequency (RF) beams and transmit the responsesignal back to the beacon.

In another example, this technology can be used for determining alocation of an end user node relative to the at least one beacon. Onemethod can include at least one beacon scanning each of a plurality ofsegments in an arc with a separate narrow radio frequency (RF) beamtransmitted. The arc is in a direction of the end user node. The atleast one beacon can receive a response signal from the end user nodebased on a received narrow RF beam at the end user node. The technologycan determine at least one of an angle-of-arrival (AOA) and atime-of-flight (TOF) of the response signal, and calculate an end usernode location relative at least one beacon location using at least oneof the AOA and TOF of the response signal.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the disclosure will be apparent from thedetailed description which follows, taken in conjunction with theaccompanying drawings, which together illustrate, by way of example,features of the disclosure.

FIG. 1 illustrates a perspective view of a perimeter ranging system witha plurality of beacons in accordance with an example.

FIG. 2 illustrates a perspective view of a perimeter ranging system witha beacon in accordance with an example.

FIG. 3 illustrates a diagram of a ranging system using angle-of-arrival(AOA) and time-of-flight (TOF) information in accordance with anexample.

FIG. 4 illustrates a block diagram of a ranging system using a 1×8antenna array in accordance with an example.

FIG. 5 illustrates a notional depiction of a beacon in accordance withan example.

FIG. 6 illustrates a notional depiction of an electronically scannedantenna (ESA) array antenna with attenuator in accordance with anexample.

FIG. 7 illustrates a notional depiction of an electronically scannedantenna (ESA) array antenna without attenuator in accordance with anexample.

FIG. 8 illustrates a block diagram of determining a time of flight (TOF)using a rising resistive capacitive (RC) voltage in accordance with anexample.

FIG. 9 illustrates a diagram of an electronically scanned antenna (ESA)in accordance with an example.

FIG. 10 illustrates a bottom view of an electronically scanned antenna(ESA) laminate layout in accordance with an example.

FIG. 11 illustrates a perspective view of building penetration of aranging system in accordance with an example.

FIG. 12 illustrates a multi-path signal and side-lobe of a beacon of aranging system in accordance with an example.

FIG. 13 illustrates a graph of atmospheric radio frequency (RF)attenuation as a function of elevation in accordance with an example.

FIG. 14 illustrates a graph of atmospheric radio frequency (RF)attenuation as a function of elevation in accordance with an example.

FIG. 15 illustrates a graph of dielectric loss as a function of radiofrequency (RF) and temperature in accordance with an example.

FIG. 16 illustrates a graph of an atmospheric absorption plot inaccordance with an example.

FIG. 17 illustrates a diagram of a graphical user interface (GUI) inaccordance with an example.

FIG. 18 depicts a diagram for reducing scanning time by reducing anumber of messages or by reducing a dwell time in a handshaking protocolvia messaging including received signal strength indicator (RSSI) orreceived signal strength (RSS) information in accordance with anexample.

FIG. 19 depicts a flow chart for reducing scanning time by reducing anumber of messages or by reducing a dwell time in a handshaking protocolvia messaging including received signal strength indicator (RSSI) orreceived signal strength (RSS) information in accordance with anexample.

FIG. 20 illustrates a graph of AoA error relative to beam pairseparation in accordance with an example.

FIG. 21 illustrates a graph of AoA error relative to beam pairseparation in accordance with an example.

FIG. 22 depicts a flow chart of a method for communicating between anend user node and a control station controller used in determining alocation of the end user node relative to a beacon in accordance with anexample.

FIG. 23 depicts a flow chart of a method for determining a location ofan end user node relative to the at least one beacon in accordance withan example.

These drawings merely depict exemplary embodiments of the disclosure,therefore, the drawings are not to be considered limiting of its scope.It will be readily appreciated that the components of the disclosure, asgenerally described and illustrated in the figures herein, could bearranged, sized, and designed in a wide variety of differentconfigurations. Nonetheless, the disclosure will be described andexplained with additional specificity and detail through the use of theaccompanying drawings.

DETAILED DESCRIPTION

It is to be understood that this disclosure is not limited to theparticular structures, process steps, or materials disclosed, but isextended to equivalents as would be recognized by those ordinarilyskilled in the relevant arts. Alterations and further modifications ofthe illustrated features, and additional applications of the principlesof the examples, which would occur to one skilled in the relevant artand having possession of this disclosure, are to be considered withinthe scope of the disclosure. It should also be understood thatterminology employed herein is used for the purpose of describingparticular embodiments only and is not intended to be limiting. The samereference numerals in different drawings represent the same element.

It must be noted that, as used in this specification and the appendedclaims, the singular forms “a,” “an,” and “the” include plural referentsunless the context clearly dictates otherwise. Thus, for example,reference to “an aperture” includes one or more of such openings,reference to “battery” includes reference to one or more of suchdevices, and reference to “applying” includes one or more of such steps.

In describing and claiming the present disclosure, the followingterminology will be used in accordance with the definitions set forthbelow.

As used herein, “substantial” when used in reference to a quantity oramount of a material, or a specific characteristic thereof, refers to anamount that is sufficient to provide an effect that the material orcharacteristic was intended to provide. Therefore, “substantially free”when used in reference to a quantity or amount of a material, or aspecific characteristic thereof, refers to the absence of the materialor characteristic, or to the presence of the material or characteristicin an amount that is insufficient to impart a measurable effect,normally imparted by such material or characteristic.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary.

Numerical data may be expressed or presented herein in a range format.It is to be understood that such a range format is used merely forconvenience and brevity and thus should be interpreted flexibly toinclude not only the numerical values explicitly recited as the limitsof the range, but also to include all the individual numerical values orsub-ranges encompassed within that range as if each numerical value andsub-range is explicitly recited. As an illustration, a numerical rangeof “about 0.6 mm to about 0.3 mm” should be interpreted to include notonly the explicitly recited values of about 0.6 mm and about 0.3 mm, butalso include individual values and sub-ranges within the indicatedrange. Thus, included in this numerical range are individual values suchas 0.4 mm and 0.5, and sub-ranges such as from 0.5-0.4 mm, from0.4-0.35, etc. This same principle applies to ranges reciting only onenumerical value. Furthermore, such an interpretation should applyregardless of the breadth of the range or the characteristics beingdescribed.

As used herein, the term “about” means that dimensions, sizes,formulations, parameters, shapes and other quantities andcharacteristics are not and need not be exact, but may be approximatedand/or larger or smaller, as desired, reflecting tolerances, conversionfactors, rounding off, measurement error and the like and other factorsknown to those of skill in the art. Further, unless otherwise stated,the term “about” shall expressly include “exactly,” consistent with thediscussion above regarding ranges and numerical data.

In the present disclosure, any steps recited in any method or processclaims may be executed in any order and are not limited to the orderpresented in the claims. Means-plus-function or step-plus-functionlimitations will only be employed where for a specific claim limitationall of the following conditions are present in that limitation: a)“means for” or “step for” is expressly recited; and b) a correspondingfunction is expressly recited. The structure, material or acts thatsupport the means-plus function are expressly recited in the descriptionherein. Accordingly, the scope of the disclosure should be determinedsolely by the appended claims and their legal equivalents, rather thanby the descriptions and examples given herein.

FIG. 1 illustrates an example ranging system (e.g., a terrestrialperimeter ranging system) with a plurality of beacons 110A-C external toa perimeter of a building 150. The ranging system can provide alocation, biometric information, and other information of an end usernode 130 (e.g., person or object) within a perimeter (e.g., thebuilding) or specified range from the beacons, where global positioningsystem (GPS) or other location services may be unreliable orunavailable, such as a victim, policeman, soldier, fireman or otherasset in a burning building. Location services can be unreliable orunavailable because of obstructions due to construction materials suchas concrete and steel in large commercial or industrial buildings, thickundergrowth in an outdoor environment, or where GPS is non-functional.The ranging system can be setup “outside” a perimeter of interest (e.g.,a building) using non-intrusive radio frequency (RF) technology. Theranging system can be used in a reactionary “first responder” situationwithout a priori (e.g., prior knowledge) of a building, structure, orarea. In an example, the ranging system can operate using portable,self-powered equipment that is independent of local infrastructure, suchas equipment that can be power via battery, generators, solar, or otherpower source besides commercial grid power. The ranging system canprovide current and historical location information of the user node(e.g., end user node, object, or person) without direct monitoring orinteraction from an operator.

The ranging system can include various components, such as an end usernode 130, beacons 110A-C, and a control station 120. The end user nodecan include a small, low power transceiver card or device with anomni-directional antenna, which can be placed on each person or objectto be tracked. The transceiver card or device can be integrated into amobile phone, tag, or other portable electronic device. The transceivercard can be a rugged, inexpensive, and mass production oriented device.One to several hundred user nodes can be tracked by the ranging system.

The beacons 110A-C (e.g., perimeter beacons) can provide RF ranging andcommunications modules outside the target operational environment (e.g.,on the perimeter). The beacons can configured to scan 140A-C segments ofan arc (e.g., a raster scan pattern) with a narrow radio frequency (RF)beam and receive a response signal from an end user node in at least onesegment. Each segment of the arc is scanned at a specified timeinterval. For example, each segment may represent 2 degrees (2°) in thearc and the arc may represent a section of a circle or sphere to bescanned, such as 120 degrees (using spherical coordinates). Although 2°per segment can be useful, arc segments can functionally range fromabout 0.2° to about 20°. The raster scan pattern can include incrementsin two axes, such as horizontal and vertical axes. Additional beaconscan provide an expandable network to meet the size of aperimeter-of-interest. One beacon can be capable of a totalgeographical-location (geo-location) capability. However, two tohundreds of beacons can be used depending on the perimeter size or areato be covered. Additional beacons can improve location accuracy.

The control station 120 can link the beacons together using a local areanetwork (LAN) to generate ranging information. The control stationprovides command center operation for node tasking and ranginginformation. In an example, the control station can be essentially a“loaded” laptop with an interface box to the beacons and the internetusing an internet protocol (IP). Although, the control stationillustration shows a separate antenna from the laptop used tocommunicate with the beacons in the LAN, the antenna can be integratedin a laptop architecture. The control station can be configured togenerate an end user node location relative to a beacon location bycommunicating with at least one beacon. The control module can beconfigured to calculate an angle-of-arrival (AOA), a time-of-flight(TOF), or both the AoA and the TOF of a response signal from the enduser node via the beacon. In an example, the ranging system can use theZigBee protocol (i.e., Institute of Electrical and Electronics Engineers[IEEE] 802.15.4 or IEEE 802.15.4-2003 compliant), offset quadraturephase-shift keying (OQPSK) modulation at 2.4 gigahertz (GHz), wirelesslocal area network (WLAN), advanced encryption standard (AES)encryption, or external amplifiers (e.g., high power amps [HPA] and lownoise amps [LNA]).

FIG. 2 illustrates another embodiment of the ranging system using acontrol station 120 and a single beacon 110. The AoA 142 and the TOF 144of an emitted narrow radio frequency (RF) beam 140 and/or a receivedresponse signal from an end user node 130 can be used to generate thelocation of the end user node. Thus, the position of the end user nodecan be determined using a single beacon as described in more detailbelow.

As illustrated in FIG. 3, the ranging system can providegeographical-location (geo-location) capability with a resolution withina meter at a 100 meter distance from transceiver beacons 110 A-C, whichcan locate the user node (e.g., person 132 or object) inside an area orperimeter, such as a cafeteria, an arena, a hotel, a school, a hardwarestore, a stadium, a park, a wilderness area, a ship, and a water front.The perimeter ranging system uses narrow RF beams 140A-C generated by anelectronic-scanned-array (ESA) antenna or phased-array antenna at thebeacon which can scan across and up and down a perimeter of interest,such as a building, using angle-of-arrival angles 142 and/or time offlight (ToF) range distances 144 to triangulate if applicable anddetermine position. This relates to the angle-of-arrival (AoA)algorithms (described herein) which provides lateral range resolutionclose to 10% of the ESA beam width; which for example a 5.6 degreebeamwidth at 100 meters distance gives 1 meter cross resolution. Thegeolocation capability also relates to the time-of-flight (ToF)information in collaboration. The rising time constant implementation isdescribed herein, for example, to provide 1 meter distance accuracy as afunction of accurate mapping of the charging voltage against time ofpropagation. Another factor which applies to ToF is the empiricaldetermination and subration of the latency through the end user node.Yet another variable is the step size capability of the analog todigital (A/D) convertor which limits the resolution steps. The compositeAoA (angle) and ToF (distance) provide a total three dimensionalgeolocation solution provided by one beacon. Multiple beacons may alsobe used in triangulation to provide best solution fits, increasing thearea of coverage, accuracy and reliability.

In the angle-of-arrival (AoA) location solution, the array antenna canprovide a narrow beam which can electronically scan across theperimeter-of-interest, where the antenna is fixed but different beamsare formed from the phase shifting of the signal by the apertures of theESA antenna. The signal can be similar to radio detection and ranging(RADAR), except that the beam may be not reflected for determining therange. Instead, the narrow beam signal can received by the end usernode, and upon interrogation by the beacon, the end user node can returnan RF signal to the interrogator (i.e., beacon). The three dimensionalangle of the narrow beam emitted and received by the ESA antennainherently gives directionality. The received signal strength (RSS) ofthe narrow beam can be measured by the end user and the RSS of theresponse signal from the end user node can be measured by the controlstation. The RSS measurement of the narrow beam can be included in theresponse signal. When the response signal is returned and identifiedwith an end user node and specified AoA, the AoA having the greatestreceived signal strength indicator (RSSI) strength can be used todetermine the angle of the end user node to the beacon. Two or more ofthese beams can produce angle projections that intersect at the locationof the end user node (as shown in FIG. 1), thus providing a totalgeo-location solution. The narrow beam can also provide a significantbi-directional RF gain (e.g., 20-30 decibel [dB]) for the signal used topenetrate the building or other obstruction. The decibel (dB) is alogarithmic unit that indicates the ratio of a physical quantity(usually power or intensity) relative to a specified or impliedreference level. Thus, a ratio in decibels is ten times the logarithm tobase 10 of the ratio of two power quantities.

In the time-of-flight (ToF) location solution, each beacon can measurethe ToF of the signal from the interrogated end user node to beacon or around trip signal path from the beacon to the end user node back to thebeacon. In another example, the end user node can measure the ToF of thenarrow beam from the beacon and return the measurement in the responsesignal or message. The ToF information can allow the determination ofthe distance to the end user node. Multiple beacons (e.g., three beaconsin FIG. 3) with ToF information can then ‘triangulate’ andsimultaneously solve for the location to derive the end user node's(e.g., person's 132) geo-location. A single beacon having both AoAdirectionality and ToF distance can be configured to derive an end usernode's position (as shown in FIG. 2). Multiple beacons can confirm thelocation information and provide enhanced reliability and accuracy (asshown in FIG. 1).

FIG. 4 illustrates a narrow pulsed beam 140 from an antenna array 160(e.g., an ESA antenna with a plurality of apertures 164) that canpenetrate an outside wall 152, which can usually have the most metal,and therefore the most RF shielding (e.g., typically 8 dB loss). Innerwalls typically have a minor contribution to attenuation (e.g., <1 dBper wall). However, building walls, ceilings, floors and other materialscan attenuate RF signals. The high intensity directional phased-arraynarrow RF beams or pulses can be capable of penetrating most buildingconstruction and foliage obstructions with over a 70 dB link budgetmargin of penetration (in addition to approximately 51 dB free spaceloss). Due the reciprocity properties of antennas, the antenna can emita high intensity directional phased-array narrow RF beam in a specifiedphase-shifted direction and can receive a weak signal from theomni-directional antenna in a direction of the specified phase-shifteddirection. A link budget is an accounting of all of the gains and lossesfrom the transmitter, through the medium (e.g., free space, air,obstruction, cable, waveguide, or fiber) to the receiver in atelecommunication system. The link budget accounts for the attenuationof the transmitted signal due to propagation, as well as the antennagains, feedline and miscellaneous losses. The enhance RF signal strengthof the phased-array antenna (e.g., the ESA antenna) can have anincreased intensity by 3 orders of magnitude (×1000 or 30 dB) over anomni-directional antenna. The omni-directional antenna can generate areduced signal power response in an omni-directional beam 146. In anexample, the narrow beams in a raster pattern scan can carry aninterrogation message which can received and responded to automaticallyby the end user node (carried by a person 132A-B or object of interest),inside the perimeter. The information of the person's location,direction of travel 134A-B and/or status can be communicated back thru asecure (encrypted) dedicated network to a control and command center,which initiated the inquiry. In an example, the perimeter ranging systemcan provide user node ranging for up to 7-8 levels of a typical buildingstructure. In an example, the control station can include a graphicaluser interface 122 (GUI) for tracking the end user nodes. The beacon caninclude a beacon ESA ZigBee module for communicating with the controlstation via the LAN, generating the RF signals 190 for the antennaarray, and providing signals for the beam forming network 178.

In an example, the beacons 110 can have at least two antennas, includingan ESA antenna 162 and an omni-directional antenna (e.g., a monopoleantenna 182 or multiple input multiple output [MIMO]). The ESA beamantenna which can include an array of radiator elements 164 can supportthe ranging functions. The omni-directional antenna can support the meshnetwork, attitude information, and communications to the controlstation. The beacon can include transceivers and a ranging and ESAantenna control electronics module 184 used to generate the narrow beamsfor scanning and for communication with the control station an antennas.The beacon can include an antennas and hardware platform 180 for housingthe transceivers and ranging and ESA antenna control electronics moduleand supporting the antennas. The ESA antenna can be used for scanningwith a narrow beam (for AoA ranging). The ESA antenna can create a 30 dBisotropic (dBi) high bi-directional gain to penetrate aperimeter-of-interest, such as an external wall. The dB isotropic (dBi)is the forward gain of an antenna compared with the hypotheticalisotropic antenna, which isotropic antenna (e.g., omni-directionalantenna) uniformly distributes energy in all directions.

FIG. 6 illustrates radiator elements 164 (e.g., radiator apertures orapertures) of an ESA antenna 162 and a beam forming network 178A on aback side of the radiator elements. The beam forming network can includean RF input/output receiver 192, a splitter and summer module 168, abeam controller 166A, phase shifters 170 for each radiator element, andattenuators 172 for each radiator element. When the ESA antenna emits asignal, the RF input/output module can receive a RF signal or message,which can be formed into a beam. The splitter and summing module cansplit an output signal from the controller or processor (of controlstation or beacon) to the phase shifters. Each phase shifters can shiftthe phase of the signal to form a composite signal with an increasepower gain in specified direction. The beam controller can be used toindicate an amount of the phase shift for each of the phase shifters anda magnitude of the signal power for each attenuator. The signal fromeach attenuator is sent to the radiator elements that emit the signal.The RF attenuators can be used to reduce side-lobes associated with beamforming.

When the ESA antenna 162 receives a signal via the radiator elements164, the signal is transmitted to the attenuators, which attenuates thesignals associated with side-lobes. The attenuators transmit the signalsto the attenuated signals to the phase shifters, which phase shifts eachreceived signal to concentrate the received signal into a compositesignal with an increase power gain in specified direction. Each phaseshifted received signal is transmitted and combined or summed by thesplitter and summing module to form the concentrated composite signal,which is transmitted to the RF input/output module. The RF input/outputmodule provide the received concentrated composite signal to thecontroller or processor (of control station or beacon), which can beprocessed.

FIG. 7 illustrates a beam forming network 178B without attenuators and abeam controller 166B configured to indicate an amount of the phase shiftfor each of the phase shifters. The attenuators can be effectivelyomitted with a software implementation that uses RSSI signal strength toidentify the main lobe without significant adverse affects from sidelobes and reflection. In particular this implementation with removal ofthe attenuators lowers the noise figure of the receiver system andincreases the system RF power output. The ESA antenna (with the controlstation) can use a RSSI determination instead of RF attenuators normallyused on ESA antennas. Eliminating the attenuators can also reduce thecost of the ESA antenna and simplify the generation of the narrow beamand reception of the response signal. The ESA antenna can generate apulse signal using phase shifters control with a ZigBee protocol. A RFand direct current (DC) signal flow can be used to control the directionof the pulsed signal, and timing can be used to hold a position forround trip signal path plus a guardband time before proceeding to thenext scanning angle (e.g., segment) in the arc. The ESA antenna includesa signal splitters/summers 168, phase shifters 170, and radiatorelements 164 and the beam controller. In an example, the ESA antenna canprovide ±60 degrees horizontal scanning and up to ±45 degree verticalscanning.

In an example 5×5 array ESA antenna with 5 apertures per array with 25apertures total measuring approximately 12.3 inches across operating a2.4 GHz frequency band, the ESA can provide a 3.5 meter (m) rangeresolution at a 100 m distance. The beamwidth Φ for each beam can havean angle θ approximately 20.3 degrees with an antenna gain magnitude of63 (i.e., 18.0 dBi). In an example 20×20 array ESA antenna with 20apertures per array with 400 apertures total measuring approximately49.2 inches across operating a 2.4 GHz frequency band, the ESA canprovide a 0.9 m range resolution at a 100 m distance. The beamwidth Φfor each beam can have an angle θ approximately 5.1 degrees with anabsolute antenna gain of 1006 (i.e., 30.0 dBi). Increasing the number ofapertures can increase the resolution, increase the antenna gain, andreduce the beamwidth. The scanning angle for an example ESA antenna canbe up to +/−60 degrees sideways and +/−45 degrees vertical with ascanning rate and dwell times adjusted for efficient operation.

The following provides additional details of the examples. The rangingsystem can provide an information oriented service focused on providingthe location and well being of people or objects, where GPS or otherlocation services are typically unreliable or unavailable. The rangingsystem can use hardware outside of the building (or an area of interest)in a nonintrusive manner using RF technology.

Some applications for the ranging system can include services primarilydesigned for “first responder” situations, where a portable rangingsystem configured to operate off an independent power source orcommercial grid power can be temporarily and quickly installed aroundthe outside perimeter of a building (or an area of interest). In morepermanent situations, the ranging system can provide a secondary system,which can be installed in a proactive manner. In such cases, the rangingsystem may provide services ahead of anticipated needs or for ongoingsituations. In reconnaissance applications, the ranging system canprovide the ability to guide a field agent or party to the location ofanother end user node inside the perimeter of interest. Guiding a partycan be performed by knowing the location of both parties andcommunicating the directions to the party in real time. In surveillanceapplications using the ranging system, the services may provide currentand historical location of an object or person, without any interactionrequired, inside of a perimeter of interest, which can include asurveillance capability of gathering positioning information about aperson without his or her knowledge. The ranging system can be used forsafety, security, strategic, and general tracking purposes for thegovernment, military, and companies of all sizes that wish to trackpersonnel, inventory or other equipment.

The ranging system can be portable, self powered, and independent oflocal infrastructure “tie ins”. No internal building or area installmentrequirements are typically used in the ranging system, except for asmall radio transceiver node (e.g., end user node) carried by a clientuser. In some applications, the ranging system can be permanentlyinstalled in, on the roof, in the attic, or crawl space of any buildingof any size. The ranging system may be installed and operated on or in avehicle or trailer, boat, plane, or any other moving craft. The rangingsystem can be designed for rugged commercial, industrial or militaryenvironments, including harsh weather conditions, such as rain, wind,temperature, and other harsh conditions. For example, in an emergencysituation, such as a building on fire, the ranging system can locateindividual firemen inside a burning building. GPS can be unreliable inmany if not most commercial buildings, and any existing infrastructurewith location services would be incapacitated or undependable during afire where power can be compromised or heat can destroy existingcommunication infrastructure systems.

The ranging system can include using narrow RF beams, which scan acrossand up and down a perimeter of interest, such as a building. The highintensity rays can be capable of penetrating most building constructionand foliage obstructions. The beams can carry an interrogation messagewhich is received and responded to automatically by a node carried by afield agent of interest, inside the perimeter. The information of theperson or object carrying the end user node, including an end user nodelocation and a status can be communicated back thru a secure dedicatednetwork to a control and command center (e.g., control station), whichinitiated the inquiry.

In an embodiment, the ranging system can include hardware components,software and systems operations as previously depicted in FIG. 1. Theprimary components can include an end user node 130, a perimeter beacon110A-C, and control station 130. The end user node can include a smalltransponder card or device placed with each person, other device, orobject to be tracked. The perimeter beacons can include RF ranging andcommunication modules outside a theater of operation on a perimeter ofan area to monitor. The control station can provide command centeroperations for node tasking and generating ranging information.

The beacons 110A-C can interconnected with a mesh grid protocol thatallows expansion as required to cover the desired perimeter. A mesh gridprotocol or a mesh networking topology can be a type of networking whereeach node not only captures and disseminates its own data, but can alsoserve as a relay for other nodes. Thus, the each node collaborates topropagate the data in the network. In an example, one beacon can providecomplete geo-location of an individual. In other examples, three toupwards of dozens or even hundreds can be used to locate the end usernode. Buildings common in industrial park areas may typically need ahalf to full dozen beacons to adequately cover the perimeter ofinterest. More beacons may be added or subtracted according the need fortotal coverage, accuracy and reliability. The thickness and type ofwalls and other obstruction in the RF beamwidth path of propagation areadditional considerations, where there may be value added with increasedbeacons. The ranging system can then more effectively use a beacon'spulse RF energy inside the perimeter with narrow beams to scan acrossthe area looking for end user nodes within the perimeter.

The nodes can include small transceivers carried by the client users(e.g., field agents, firemen, etc.) or placed on objects to be tracked.The nodes can have active electronics which respond to the RF inquiries.Two types of ranging information can be collected including thedirectionality angle towards the end user node (e.g., the client user),and/or the range distance to the end user node. Client biometrics mayalso be monitored. The collected data can be routed to the controlstation, which can provide the processed information to the operator viaa user interface. Data inquiries can originate from the control station.The control station can be near the operational perimeter, or commandedoffsite via internet access or other remote monitoring technologies.

The components of the ranging system can communicate via a ZigBeeprotocol, or more formally known as an Institute of Electrical andElectronic Engineers (IEEE) 802.15.4 standard. The ranging system caninclude RF transceiver and microcontroller integrated components,programmers, emulators using the ‘C’ language programming, althoughother programming languages can be used. As other protocols can supportthe functionality of the ranging system, the ranging may use protocolsand associated hardware, in addition to or instead of the ZigBeeprotocol.

A RF transceiver using the ZigBee protocol can operate with offsetquadrature phase-shift keying (OQPSK) type modulation at 2.4 gigahertz(GHz), which can be acceptable anywhere in the world. Frequencies otherthan 2.4 GHz can also be considered and implemented to address specificand/or custom needs of clients. The ranging system can implement theZigBee low duty cycle of network time gated pulses, which can facilitatetransmit and receive functions, and also reduce battery use. The rangingsystem can use sequential spread spectrum modulation which can minimizeinterference from hostile outside RF sources. Advanced encryptionstandard (AES) type encryption can be for added security againstattempted tampering.

In an example, the ranging system can form a standalone ZigBee localarea network (LAN) or wireless LAN (WLAN) with an expandable meshnetwork. The network can be adapted to the sizing requirements of anysize building or area extending to a mile or more (with less stringentspecifications).

Information services related to the ranging system can obtaininformation regarding people in a remote fashion and discrete manner,thru building walls or other obstructions. The services can be obtainedby establishing an infrastructure external to the perimeter-of-interestwhere the person or persons may be located. Radio waves can be used topenetrate inside the perimeter. In the ranging system architecture,nothing physically inside the perimeter related to the system isrequired to exist except for a small transponder node (e.g., the enduser node) placed on the end user.

The ranging system can provide location information of field agents thatmay be in harm's way. The ranging system can also optionally providecommunications services. The informational services are transmitted in asecure fashion, and may also be received discretely in various displays,messages, or audible sounds. For example, the immediate geo-location ofany end user node can be available for an operator at a control station.The end user node information can be obtained automatically withoutinteraction (or notice) from the end user carrying the end user node.The accuracy can be within +/−one meter at 100 meter distance from thebeacons. In an example, the ranging system can identify which room aperson or device is in. In another example, a history of an end user'sor item's location can be obtained over a specified period of time(e.g., a 24 hour period of time) inside the ranging area. In anotherexample, the ranging system and the end user node can collect biometricinformation, such measuring and transmitting a person's heart rate,respiration, or other biometrics, which can be provided to the controlstation in an automatic fashion, or as commanded with no initiation onthe part of the client user. In an example, text messages can be sentand received from a control station to any single end user node in theLAN. The text messages can also be sent to any group preset in thesystem (e.g., security staff, field agents, or support crew). Thecontrol station can be automatically be notified if people enterunauthorized areas or if inventory leaves designated areas. Notificationcan be sent via text, email, or directly to the control station monitor.The ranging system can use several preset messages (e.g., cannedmessages), which can be available to respond to common and expectedactivities and responsibilities inside the perimeter area. For examplein a fire situation, a preset message for an end user node mightinclude: “Are you ok?” The present message can provide a quick and easyresponse in the middle of other important activities. In a more coverttype example, the present message can provide a quiet and discreteresponse to the inquiry. The messages can be sent directly to and fromthe control station and end users. Messages can be sent in voice packetsfrom or to a user node and the control station. The message can betransmitted via half-duplexing or voice over IP (VOIP). Another voicemessage can include a message that can be sent, which can be activatedafter a specified wait time. For security reasons, the message canoptionally be set to be listened to only at the discretion andconvenience of the operator and end user, which can have an advantagesimilar to text messaging.

The end user transponder node can be used to obtain informationregarding people in a remote fashion and discrete manner, thru buildingwalls or other obstructions. The end user transponder node can include acomponent used for giving or obtaining information related to any enduser persons or objects of interest inside the perimeter. Theinformation can be routed through the ranging system's own securenetwork to a control station, directed by an operator.

The end user client node can be used as a transceiver and a transponder.The end user client node can include a high level production orientedand inexpensive component. The RF functionalities can include offsetQPSK modulation, AES encryption, and sequential spread spectrum. Thefeatures of the end user node can be used to support ranging,communications and network functions. The end user node can include asystem on chip (SOC or SoC) or a single chip solution, which can havefewer peripheral components supporting the chip. The embedded softwarecan facilitate the functionalities for receiving a narrow radiofrequency (RF) beam inquiry message or signal, transmitting a responsesignal, and processing and generating signals according to other rangingsystem functions. The node can include additional circuitry, such asexternal amplifiers (HPA & LNA), which can be used to meet system RFdynamic range requirements. The peripheral amplifier components willenhance the performance for both transmitting and receiving. The enduser node can include two antennas which can provide the desiredpolarization and positional diversity. The two antennas can help securea lock on the end user node as the user moves around, and the user'sbody affects the RF antenna radiation.

The end user node can be included in a handset or badge style componentwith a secure means of attaching the node to the end user. The use andoperation of the node may extend only in a specified perimeter or areasof operation. The node may be registered and operational with aspecified ranging system. In an example, several hundreds of user nodesmay be transmitting signals to beacons and receiving signals frombeacons inside a perimeter. The end user nodes can be rugged, light andsmall, which can be powered by small style batteries and easily charged.

The control station can include a component used for generating andobtaining information related to the end user node of interest insidethe perimeter. Information can be routed through the ranging system'sown secure network to the control station, directed by an operator.

The control station can include the command and control center. Thecontrol station can provide the end point for the mesh grid networkrouting from the beacons. The beacons can pass ranging and otherinformation to and from the control station to each other and the enduser nodes. The control station can be portable and, like the beacons,can be outside the perimeter of operation. FIG. 1 shows a notionalsignal routing and positioning of the control station relative to othercomponents, the beacons and transponder nodes (e.g., end user nodes).The functions of the control station can include supporting a networkaround a perimeter of interest, providing location information aboutfield agents inside the perimeter of interest, providing biometricsinformation about field agents, and providing two-way communication invarious modes to field agents.

In an example, the control station can be communicatively couple to thebeacons via an external network, such as an internet interface box tothe world-wide-web (www). LAN signals used by the on-site controlstation can be configured with security protocols to operate via theInternet or other external network. Software used for accessing andusing the information can be loaded thru a USB port to authorizedcomputers. Authorized operators can have password encryption controlledaccess via IP to the command ranging systems features. The encryptionand other protocols can allow access and operation to a virtual controlstation at a location of convenience with internet access.

The control station can include a graphical user interface (GUI)designed for convenient operation so an operator can use the rangingsystem with minimal training. Location and communications interrogationsof end users node can be made via the GUI or control station. Group aswell as individual messages can be sent to persons with a transpondernode.

The GUI can be configured to adapt to and construct various perimetersof interest. The control station and/or GUI can be used to model anarea, such as a large manufacturing building for example, in a veryshort time. The control station and/or GUI can be used to map a buildingfor monitoring, which can be integrated into the location algorithms ofthe ranging control center system (e.g., ranging system).

The control station can be configured to show the location and movementhistory of the end users inside the perimeter of interest. The controlstation can be configured to provide biometrics of the field agents andvarious modes of secure communication, particularly of a discretenature, if desired. Software processing can be designed to performfunctions such as simultaneous matrix equation solving and triangulationfor ranging solutions with information gathered from the respectivebeacons and user nodes.

Ranging solutions can be used to perform the geo-location of people orobjects, such as locating people or objects thru building walls andconstruction, as well as outdoors in thick vegetation or areas obscuringvisibility. The ranging solutions can be provided by a ranging systemwhere a global positioning system (GPS) or other existinginfrastructures may be unable or unreliable.

FIG. 2 shows a pictorial representation of beacons 110A-C external to aperimeter used to determine the location of an end user 132. The duallocating capabilities can be used by each beacon. The narrow beam from aplatform, such as a beacon, can singly aid in providing angle-of-arrival(AoA) directionality towards a person of interest (e.g., an end userclient node). As such, two or more beams may be to find an intersectionof beams used to determine an individual's location. However, a secondmeans of ranging can also be obtained from each beacon, using atime-of-arrival (TOF) technique which can generate a distancemeasurement. Thus, knowing both the angle and the distance can alloweach beacon to geo-locate an end user node independently of otherbeacons. Furthermore, additional beacons focused on an end user node canprovide enhanced accuracy and reliability to the system.

The beam width of the beacon can provide an enhanced RF signal strength.As the beam narrows, as compared to an omni-directional beam pattern,the narrow beam's intensity increases two to three orders of magnitude(×1000 or 30 dB). Due to the reciprocity of antenna operation the gainis generated both in the transmission and the reception. The RF signalstrength can be sufficient to penetrate inside the perimeter, such as alarge industrial grade building or dense foliage outdoors. The dualsolution of calculating the AoA and TOF of a narrow beam can provideaccurate and reliable ranging information.

In an example, the ranging solution can be based upon the use of ZigBeeintegrated circuitry, even though positioning or geo-location is not anormal part of the ZigBee protocol. ZigBee was established for datacommunications and information transfer services. However, the IEEE802.15.4 configuration can supports radar like features having a pulsedtransmit and/or receive switching functionality. The time slot protocolcan allow using a similar frequency back and forth (e.g., a downlink anduplink) with a same antenna with minimal filtering. A substantially sameprotocol can be compatible with the bi-directional requirements of theESA antenna in the beacons used for AoA ranging. With modifications tothe protocol the ranging system can also accommodate a TOF rangingimplementation.

A dual ranging capability can be provided for, using two solutions,integrated into the ZigBee circuitry. In an example, the totalgeo-location solution can provide +/−1 meter degree ranging accuracy at100 meters distance from the control station.

The range solutions can be relative to each beacon in contact with atargeted user (e.g., end user node). The range solutions can generatemagnitude values (related to meters) for the TOF solution, and threedimensional ‘vector’ values (in degrees) for the AoA solution. Therelative range values can be used to derive absolute geo-locationpositioning via averaging.

Accurate attitude (i.e. positioning and pointing) information of eachbeacon can be determined and sent with the dual ranging data to thecontrol station for processing and a total geo-location extraction.

In an example TOF solution, ranging can determined directly withpropagation timing measurements or tone ranging and phase determination.The associated hardware circuitry can be tied into the beacontransceiver structure. Any impacts to the end user node may be minimalto the hardware, and may be related to software encoding. The TOFsolution can typically provide +/1 m distance stand alone positioningaccuracy.

In an example AoA solution, directionality can be provided by a narrowradio beam which scans across the perimeter of interest. The beam can becreated from an electronically scanned phased array antenna in eachbeacon. Gimbals may not be used on the ESA antenna gimbals cannot scanfast enough and the gimbals can be too expensive and not rugged enoughfor portable applications. Scanning can be performed in threedimensional space (i.e. in two planes). In an example, the AOA solution,which can also be stand alone solution can provide +/−1 meterpositioning accuracy at 100 meter distance from the beacon.

The beam can be narrowly focused or fan shaped in a latitude/longitudeorientation, depending on the practicality and trade-offs of theimplementation. Multiple ranging beams simultaneously sweeping from thesame beacon antenna can also be used. Simultaneous multiple rangingbeams can be generated using multiple beam forming networks on a singleantenna platform. The multiple beam forming networks can be used toincrease the update positioning rates, and also to accommodate a highernumber of end users in a given perimeter area.

In another example TOF solution, the TOF can be used to measure thecharging voltage of a circuit which is rising as a function of the timeto and from the beacon and end user node. The voltage can then bemathematically mapped to the actual distance to the node.

The operator can send an inquiry regarding the location of an end usernode. The inquiry can be routed thru the mesh network, via the beacons.At the instant a beacon sends an inquiry, a voltage pulse can begincharging a capacitor. The voltage can logarithmically charge as afunction of the RC time constant.

When the targeted node receives the inquiry, the node can send anacknowledgement back. As soon as the beacon receives theacknowledgement, an analog-to-digital (A/D) circuit can sample thecharging voltage. The charged and sampled voltage can be relatedmathematically to the time-of-flight of the radio wave propagation, andthe latency of the relayed circuitry. The control station can have aprior knowledge (i.e., foreknowledge) of the latency and knowledge ofthe radio wave's speed, which allows the distance between the end usernode and the beacon to be determined. The latency can be determined bysynchronizing the end user node clock to the bit transitions of thebeacon transmitter. Alternatively, the inquiries can be repeated enoughtimes to provide a statistical average of latency determination.

In another example, four or more beacons can each obtain scalar distanceinformation to the user node. The beacons can also be pre-determined asto their location. A mathematical matrix can provide simultaneousequation solving and beacon triangulation to determine the position ofthe desired node. Alternatively, an angle of arrival solution used inconjunction with the time of flight information can allow a completepositioning solution with a single beacon.

FIG. 8 illustrates block diagram and circuitry for determining a time offlight (TOF) using a rising resistive capacitive (RC) voltage. Themethod and circuit for determining a range (i.e., distance) from abeacon 110 to end user node 130 can be based on an indirect measurementof an RF signal that goes from the beacon to the user node and back tothe beacon. A specified resistive capacitive (RC) voltage (e.g., Vo 272)can concurrently charge logarithmically with the TOF of an inquiry 350signal and a response 352 signal, which can represent a certain amountof displaced time, which can be converted and calculated to distance.

The method directly can measure the rise time of an R/C time constantthat is charging during a time a pulse is sent from the beacon to theend user node and returns to the beacon. A beacon can send out aninterrogation 360 to user node and simultaneously begins charging apulse on an input voltage Vi 370 thru a switched capacitor 384 (SC) andresistors 380 and 382. The charging voltage can provide an input to ananalog-to-digital (A/D) convertor (ADC) 360. The user node acknowledges352 the inquiry and returns a signal which creates an incoming pulseback to the beacon. The returned pulse can stop the R/C charging intothe ADC. The measured voltage can be mathematically converted intodistance. For example, the voltage gain can be represented byVo/Vi=R2/(R1+R2+SC*R1*R2) 390. Time t 374 can be calculated from1−e(−tΣT) 394, where τ=R1*R2*C/(R1+R2) 392. The latency thru the usernode can be subtracted, and the net distance can be determined.

The beacon can be a component used for giving or obtaining informationvia an end user node related to an end user person or object of interestinside the perimeter. The information can be routed through the rangingsystem's own secure network to a control station, directed by anoperator.

The beacon component can include a series of platforms placed around aperimeter of the theater of operation. The platforms can be used tointerface with the end user nodes, the control station, and with otherbeacons.

FIG. 5 illustrates a beacon platform 100 which can include two antennas.The electronically scanned array (ESA) antenna 162 can be pulsing theend user nodes (carried by field agents) with a narrow beam (or beams)inside the theater of operation. The omni-directional antenna 182 canprovide the mesh network connectivity between beacons and the controlstation. The beacon component can act as a hub with simultaneousoperations between the end user node and the control station.

As part of the dual ranging capability, the beacon 110 can provideinformation about beacon's attitude (positioning) and pointingdirection. Different sensors, such as a GPS receiver, can be used togather attitude and/or pointing direction information. The beaconplatform can be configured to adjust the beacon's orientation for uneventerrain. The ESA antenna 162 can include an angle of adjustment, so thecenter of the antenna's scan can be midway up an area (e.g., a building)to be scanned. The attitudes setting for the beacon can include GPScoordinates (e.g., latitude, longitude, or elevation), a horizontallevel adjust, an ESA antenna rotational face direction, or an ESAantenna angle adjustment.

The ESA antenna 162 can be supported by a ranging and ESA antennacontrol electronics module 184 containing a high power amplifier (HPA)and an external low-noise-amplifier (LNA). The HPA can be used toincrease the output power to 1 Watt, which is the max power allowed forthe antenna by the Federal Communications Commission (FCC). The externallow noise amplifier (LNA) can improve the receiver sensitivity. Theenhanced dynamic range for both transmit and receive ends can insure theranging functionality. The signal from the ranging and ESA antennacontrol electronics module can combine with the high RF gain of the ESAantenna to provide a powerful penetrating RF beam into and out of thetheater-of-operation. The RF components to support the communicationsand mesh net grid functions via the omni-directional antenna may notneed the high performance of the dual range circuitry used in the ESAantenna. The omni-directional antenna (e.g., a quarter wave whip or halfwave dipole) can provide connectivity between the beacons and thecontrol station.

The array antenna (e.g., electronic scanned array (ESA) antenna) canprovide a narrow scanning RF beam which can provide angle-of-arrivalpositioning information. The array antenna can provide at least onebeam, and may provide several beams for enhanced performancecapabilities. The ESA can provide a high RF gain which can accompany thenarrowness of the beam width, which can be to penetrate thru‘perimeters-of-interest’ such as buildings with thick construction, oroutdoor areas of heavy foliage.

The ESA antenna can be used to scan across and up and down the perimeterof interest at a rapid rate and can communicate with an end user RFtransponder node. The ESA antenna can operate in both a transmit andreceive mode. The ESA antenna can be included in the beacon, which canprovide a platform for the ESA antenna structure. FIGS. 6-7 show blockdiagrams of basic components for the ESA antenna. The ESA antenna caninclude signal splitters/summers 168, phase shifters 170, attenuators172, and radiator elements 164. Each component can be bi-directional toallow for both transmit and receive. In an example, the ZigBee protocolcan be used to provide for pulsed switching time intervals betweentransmit and receive at closely spaced frequencies. Pulsed switchingtime interval can reduce filtering and provide compatibility to a singleport antenna with dual transmit and receive functionality.

The splitters 168 can divide the signal from the transmitter into thenumber of signals to feed each antenna aperture. Received signals intothe beacon, in the receive mode, from each of the apertures can besummed together by the same circuitry before entering the LNA. For thesake of both paths, the splitter/summer circuitry can be low losscircuit. In an example, the splitter/summer circuitry can includemicrostrip copper etchings for performance as well as costconsiderations.

The attenuators 172 can be used to reduce the side lobes, which in anexample can be −13 dBi without the attenuators. However, attenuators canalso degrade the noise figure and decrease RF power output. In someapplications, side lobes can generate a false lock onto the end usernode during the antenna scanning, which can generate inaccurate AoAinformation. FIG. 7 shows a beam forming network with attenuatorsomitted. Instead of attenuators, an RSSI indicator capability can beimplemented, which can provide a true lock to the antenna's mainend-fire lobe.

Voltage controlled phase shifter 170 components can provide the changein direction of the beam, and cause the beam to scan across and up anddown the area-of-interest. The beam controller 166A-B signals can becontrolled (at least in part) from a micro-processor in the beacon ESAZigBee module (176 of FIG. 4) (e.g., a ranging Zigbit module). The RFsignals can come to or from the antenna radiating elements or radiators.In an example, the apertures can include micro-strip etchings onto aPCB. FIGS. 9 and 10 illustrate the come of the components of thebeamforming network and the ESA antenna.

The ESA antenna can provide beam polarization. The ranging antenna beamcan be implemented using a right hand circular polarization (RHCP)antenna or a left hand circular polarization (LHCP) antenna to handlevarious position orientation of the end user antenna node. Circularpolarization of the antenna can also provide mitigation againstmulti-path ambiguities. If the signal is reflected, the reflected signalchanges to an opposite polarization. For example, a RHCP signal can bereflected as a LHCP which may not be received into the RHCP port of thereceiver. Circular polarization adds to the inherent advantage of thenarrow beam in reducing multi-path problems.

The ranging system can be installed outside the perimeter of interestusing a non-intrusive technology, such as RF technology. The rangingsystem can be portable, self-powered, and independent of localinfrastructure, which can provide current and historical location of anobject or person, without any operator or end user node interaction. Thehigh intensity rays can penetrate most building construction and foliageobstructions (e.g., up to 70 dB of penetration or gain). The beams cancarry an interrogation message which can be received and responded toautomatically by a node, carried by a field agent of interest, insidethe perimeter. The information of the end user node's location andstatus can be communicated back thru a secure dedicated network to acontrol and command center, which initiated the inquiry.

As illustrated in FIG. 2, the ranging system can provide a dual rangingsolution (e.g., AoA and ToF), which can work together to providereliability. The angle-of-arrival (AoA) solution can give an angularpointing direction towards the end user node (e.g., a field agent) usinga narrow beam (e.g., high RF gain) implementation. The time-of-flight(ToF) solution can give the distance information. Either the AoA or ToFsolution can provide total positioning by triangulation or intersectionof multiple beams from around the perimeter. Both solutions can be usedtogether from a single beacon to provide total positioning (as a standalone beacon).

In the AoA location solution, the array antenna can provide a narrowbeam which electronically scans across the perimeter-of-interest. Thesignal can be similar to radar, except that the beam may not bereflected. Instead, the signal can be picked up by the end user node,and upon interrogation can return an RF signal to the interrogator(e.g., beacon). The three dimensional angle of the narrow beam caninherently give directionality, where the signal is returned andidentified, having a greatest RSSI strength. Two or more narrow beamscan produce angle projections that intersect where the end user node islocated, thus providing a total geo-location solution. The narrow beamcan provide a significant bi-directional RF gain (e.g., up to 20-30 dB)used for the signal to penetrate the building.

In the ToF location solution, each Beacon can measure the time taken toand from an end user node interrogation. The timing information canallow the determination of the distance to the end user. In an example,three beacons with ToF information can triangulate and be simultaneouslysolved to derive the person's geo-location. A single beacon having bothAoA directionality and ToF distance can be used derive an end usernode's position. More beacons can serve as confirmation of theinformation and provide enhanced reliability and accuracy.

The ranging system can use the ZigBee protocol (e.g., IEEE 802.15.4).The RF transceivers can operate with OQPSK type modulation at 2.4 GHz,which is a widely acceptable transmission frequency throughout theworld. The ZigBee low duty cycle of pulses can minimize battery use.Sequential spread spectrum can minimize interference from hostileoutside RF sources. AES type encryption can provide added securityagainst attempted tampering. The ZigBee local area network can beexpandable to any size theater-of-operation. ZigBee is an industryworld-wide protocol that can be adapted to the ranging system. The dualToF and AoA ranging solutions are not standard in the ZigBee protocol.ZigBee was established for data communications and information transferservices. However, the IEEE 802.15.4 configuration can support ‘radarlike’ features having a pulsed transmit/receive switching functionality.The time slot protocol allows using close to a same frequency back andforth with the same antenna with minimal filtering. The time slotprotocol can be compatible with the bi-directional functionality of theESA antenna in the beacons used for AoA ranging. With modification, theZigBee protocol can accommodate a ToF ranging implementation.

The narrow beam penetration of buildings, obstructions, and otherstructures can be affected by the building materials and the signalwavelength. For example, the RF signal attenuation of the signal candecrease as the metal screening sizes decrease or as the frequencydecreases (i.e., the wavelength of the signal increases). Concreteblocks can have greater attenuation on signals than materials such aswood, plywood, or drywall (e.g., gypsum board). Frequencies above the Sband (e.g., 2.4 GHz) can propagate better thru metal screen openings(such as a stucco wall with ‘chicken wire’ mesh screening, or a chainlink fence). Frequencies below the S band (e.g., 2.4 GHz) can propagatebetter thru solid metal obstructions (such as a metal door). Thewavelength of 2.4 GHz (i.e., 12.5 cm wavelength) can be effective forbuilding penetration, and the ESA antenna generating the signal can havesmall antenna apertures. Although actual values can vary, the RFattenuation thru construction materials, such as plasterboard for a wallcan be 3 dB, a glass wall with a metal frame can be 6 dB, a cinder blockwall can be 4 dB, an office window can be 3 dB, a metal door can be 6dB, and a metal door in a brick wall can be 12.4 dB.

The narrow beam RF signal strength loss in penetrating the building canbe due to RF shielding due to construction materials used. For example,the outside wall usually has the most metal, and therefore the most RFshielding (e.g., 8 dB). The inner walls usually have a minor effect(e.g., <1 dB of RF shielding per wall). If a cell phone or mobile phoneworks inside the building, then the ranging system can also communicatewith end user nodes inside the building.

FIG. 11 illustrates a close in beacon 110D and close out beacon 110Eplacement. Floors between building levels can be constructed of metalreinforced concrete. Floors in multi-story buildings 150 can havesimilar attenuation and RF shielding to outer walls (e.g., 8 dB). In anexample with a link budget of 70 dB, the ranging system can penetrateapproximately 7-8 levels based on standard (e.g., current) constructionmaterials and practices. When a beacon 110D is close to the building thenarrow beam 140D may penetrate more floors (e.g., 1st story perimeterentry 156) to communicate with the end user node 130 with more signalattenuation, but the AoA measurements may be more accurate. When abeacon 110C is further away from the building the narrow beam 140E maypenetrate fewer floors (e.g., 3rd story perimeter entry 154) tocommunicate with the end user node with less signal attenuation, but theAoA measurements may be less accurate. In an example, some beacons canbe moved close to the building to provide smaller spreading losses andgreater AoA accuracy, while other beacons can be moved further from thebuilding, so that the incident radio beam enters the building at ahigher level, which can be a trade off of spreading loss and AoAaccuracy. Thus, in some configurations of the system, at least twobeacons are located at varying distances from another with respect tothe building.

FIG. 12 illustrates a multi-path signal 246, side-lobes 244, false lobesignal 242, and direct path narrow beam of a beacon 110 of a rangingsystem. In the scanning process, the RSSI built in feature of thetransceiver Zigbit modules can differentiate between weaker multi-pathsignals and the stronger one from the main beam. The direct path narrowbeam can have the strongest RSSI relative to the multi-path signals,side-lobes, false lobe signals. In an example, the ESA antenna can beright hand circularly polarized (RHCP). Multi-path reflections canbecome left hand polarized and as such will not be well received by anRHCP antenna.

The angle of elevation (for large over-the horizon ranges) can have aneffect on the RF attenuation. FIGS. 13 and 14 illustrate of a graphs ofatmospheric radio frequency (RF) attenuation as a function of elevationat Dulles VA with 99.9% availability. Dramatic increases in RFattenuation can occur below 20 degrees elevation. Ku and Ka bands canhave significant magnitude-of-order attenuation increases below 20degrees. Ku and Ka bands can have significantly higher RF losses overthe lower frequencies. The Ku band is the radio frequency range from10.95 gigahertz (GHZ) to 14.5 GHz or the band directly below the K-band.The 10 GHz has been recognized as a ‘dividing’ line for causingsignificant atmospheric effects on signals. In general these effectswill be less than significant especially for the intended lowerfrequencies of use and shorter ranges of operation (i.e. tens to severalhundred meters). Typically, the range of operation will be less than 300meters and often less than 100 meters, although other ranges can besuitable. The 2.4 GHz frequency band used in an example for the rangingsystem is minimally affected by water or moisture. FIG. 15 illustratesdielectric loss (e.g., heating effects of moisture) as a function ofradio frequency and temperature (0-100 Celsius [C]). Peak dielectriclosses (i.e. max absorption and heating capacity) can occur at 10-50 GHz(not 2.4 GHz). Resonances of moisture effects may not occur at 2.4 GHz.RF losses at 2.4 GHz due to moisture can be improved from the higherfrequencies where resonance occurs.

Signals can also be affected by gaseous absorption. FIG. 16 illustratesan atmospheric absorption plot. Signals at 22-25 GHz and >40 GHz canhave excessive atmospheric attenuation. Water droplets and dioxide canbe the main contributing factors for gaseous absorption. Lowerfrequencies can generally have less atmospheric attenuation. Atmosphericlosses due to moisture may not be a factor at 2.4 GHz.

Table 1 illustrates atmospheric radio frequency (RF) attenuation as afunction of the angle of elevation at Dulles VA with 99.9% availability.Lower elevation can cause increased atmospheric RF attenuation impacts.

TABLE 1 Frequency (GHz) Elevation (deg) 1 1.4 2 5 8.1 15 26.25 5 4.594.88 5.18 6.29 6.1 21.29 56.62 20 0.83 0.89 0.96 1.24 1.85 7.43 21.39 450.11 0.13 0.15 0.28 1.04 4.79 14.39 90 0.07 0.09 0.1 0.19 0.79 4.26 14.4Attenuation (dB)

Moisture effects can be common at S band frequencies. The affects offog, rain, snow, hail, and/or smog can be minimal due to the wavelengthof the IEEE 802.11a and IEEE 802.11g signals (0.17 feet (ft) and 0.41ft, respectively), which is commonly known to industry groups as WiFi.The wavelength of each type of signal can be appreciably longer than thesize of a water droplet or smoke particle, so the signal can passthrough moisture types of media with no negative effects or minimalnegative effects.

In an example, the end user node can use an IEEE 802.15.4-2003 compliantstandard operating at a 2.4 GHz RF frequency, and include AES securityencryption; XMTR RF power out at −17 to +20 dBm adjustable; −104 dBmRCVR RF sensitivity; 120 dB optimum with +20 dBm HPA dynamic range;1.8-3.6 Volt (V) supply voltage (e.g., watch batteries) internallyregulated; electrostatic discharge (ESD) robustness; ultra-low current(and power) consumption with 20 nA consumption in sleep mode, 15.5 mAconsumption in receive mode (RX), and 16.5 mA (at 3 dBm max RF output)consumption in transmit mode (TX); O-QPSK modulation; 250 kbps datarate; <1 millisecond (ms) power up time; easy interfacemicro-controllers; and −40 to 85 C temperature range.

In an example using a single dimension 1×8 antenna array (approximately4×20 inches), the ranging system can operate in quasi-real time at 2.7seconds per scan with a +/−46 degree of antenna horizontal scanning with2 degree step sizes (e.g., arc segments).

FIG. 17 illustrates a computer display of a GUI showing the position oftwo end user nodes 310 and 320 using an AoA and received signal strengthindicator (RSSI) based detection. In the example, the ranging systemscans 300 from −46 to +46 degrees every 2.7 seconds. The center of theESA antenna can be zero (0) degrees 302. The color of the display orfield can change with the strongest RSS or RSSI information received.For example, the display can automatically update users AoA (e.g.,positions) and assign a highlighted color based on the RSS or RSSIinformation (given in dBm). In FIG. 17, Unit 1 310 has a strongest RSSor RSSI at −10 degrees with a −45 dBm 312 RSS or RSSI, and Unit 1 320has a strongest RSS or RSSI at 22 and 24 degrees with a −63 dBm 322 RSSor RSSI.

The ranging system (e.g., asset tracking and monitoring system) cantrack human and other assets in real time and with high accuracy as theymove throughout an area (e.g., building). The ranging system can actwhere GPS cannot to figuratively “see thru walls”. Utilizing a controlstation monitor with a three dimensional (3D) GUI, an exact location ofend user node can carefully monitored and logged, providing anunparalleled level of security, information, reliability and safety.Besides positioning data, other information can be transmitted to thecommand station such as oxygen level, heart rate, blood pressure, oxygentank levels, and/or temperature. By secure means, the data generated bythe ranging system can also be seen by remote monitors.

The ranging system can include at least one of the following advantages,unmatched low visibility and/or indoor performance, quasi-real timeasset motion tracking, selective display of assets, ability to monitorand display biometric or telemetry data of asset, uses RF physicallynon-invasive techniques, cost effective and highly reliable, flexibilityto respond to new opportunities, and highly encrypted and secure datatransfer.

The ranging system can locate people or objects thru walls by means ofradio waves using beacons, end user nodes and the control station. Theranging system architecture can be external to the ‘perimeter ofinterest’ and thus can be non-invasive. The self contained architectureof the ranging system may not use an existing infrastructure (such asGPS, hotspots, or routers). The location information can be referencedagainst the beacons having no a-priori knowledge of the ‘perimeter ofinterest’, which can work well in a first responder safety-of-lifesituation.

The use of narrow beams of radio waves can be used for angle-of-arrival(AoA) directionality. The use of narrow beams can penetrate thick wallsor other obstructions. The rise time ToF solution can generate adistance measurement. The use of RF pulses in a frequency shared mediumcan economize the spectrum reduce direct current (DC) powerrequirements. The use of spread spectrum can minimize interference toand from other resources. The use of spread spectrum can minimize thepotential of the ranging system being electronically jammed. The use ofdata encryption can protect the information being obtained. The use oftransducers, sensors and microcontroller can be used to obtain otherinformation besides location, such as biometrics.

The ranging system and beacons can be configured to adapt the RF pulsepower to the reduced power levels needed for determining the end usernode location. The adaptive accessory use of transducers, sensors andmicrocontroller can be used to obtain other information besideslocation, such as user biometrics and node telemetry. The use of AoAwith ToF can provide a total ranging solution with high precision ofboth direction and depth. The ranging system can be configured to have atotal (3 dimensional) location fix with a single beacon. The rangingsystem can be configured to use multiple beacons to triangulateproviding enhanced reliability and accuracy. The ranging system can beconfigured to electronically scan the radio beams two dimensionally tocover large areas of space in a shorter period of time. The rangingsystem can be configured to electronically scan the radio beams in aquasi-real time fashion. The use of beacons around the perimeter canprovide total coverage. The use of beacons side by side with concurrentprobing can provide faster tracking speed and enhanced coverage. Theranging system can adapt the ZigBee protocol to send inquiry RF pulsesand receive responses. The use of received signal strength (RSS) canassist the AoA solution to locating the end user node. The rangingsystem can be configured to project where a user node will be when auser node is moving based on historical information. In an example, theranging system can dynamically change the range of the scan based onprior end user node location measurements or a predicted end user nodelocation range or area. The ranging system can be configured to expandor contract to adapt to the perimeter-of-interest. The GUI controlstation of ranging system can be configured to locate and then track theend user nodes. The GUI control station can be configured to providehistory of the end user node locations or travel. The ranging system canbe configured to provide perimeter modeling at various levels, includinga rudimentary and high fidelity level. The ranging system can beconfigured to use beacons to provide supplementary data such as videoand infra-red information. The use of manually pointing to control theESA antenna focus can be used in addition to automatically scanning. Inan example, the ESA beacon signals can operate a scanning radar modewith digital signal processing (DSP) to provide sliced picture imaginginside the perimeter (analogous to medical imaging). The scanning radarmode can use RF passive reflection rather than the use of active nodes.

In an example, the ranging system can adapt the ‘inquiry and response’handshaking protocol (e.g., ZigBee protocol) to the ‘time gating’ dwelltime windows and scanning for the RF signal. The protocol can be usedfor the ESA DC pulse antenna scanning controls. The IEEE 802.15.4configuration can be configured to support ‘radar like’ features havinga pulsed transmit/receive switching functionality. The time slotprotocol can allows using close to the same frequency back and forthwith the same antenna with minimal filtering. The ranging system canprovide multi-path and side-lobe mitigation. In the scanning process,the RSSI built in feature of a transceiver Zigbit module candifferentiate between weaker multi-path signals and the stronger onefrom the main beam. The ESA antenna can be right hand circularlypolarized (RHCP) or LHCP. Multi-path reflections can become polarizedopposite the transmission and as such will not be well received by anRHCP antenna. A shortest ToF measurement can correlate with direct pathsignal. Multiple beacons triangulating from different directions willprovide a majority vote mechanism to select the end user node location,which can produce enhanced reliability and also accuracy. In themajority vote solution, the location can be generated from the majorityof beacons correlated to a position.

In another example, the beacons of the ranging system can providesimultaneous transmission to increase throughput. The beacon controllercan be configured to support multiple simultaneous broadcasts. In anexample, a beacon antenna interface can support 4 separate connections.The beacon controller computer (e.g., a high end PC) can supportmultiple universal serial bus (USB) connections and process multipletransactions at an approximately time. In a simultaneous broadcastexample, four RF combiners can be used to couple simultaneous signals tothe antenna. The combiners can have high reverse loss, so feedbackproblems may be minimal. Multiple user nodes could be set to differentfrequencies (e.g., 4 different channels). Each receiver can be tuned toa selected frequency and can ignore the frequencies of other end usernodes. The beacon can also have multiple receivers. Each receiver on thebeacon can be tuned to a selected channel of a frequency band (e.g., theZigBee band). The bandwidth of the beacon antenna can be adequate tosupport multiple ZigBee channels. For example, the ZigBee band isapproximately 2.4 GHz and each ZigBee channel can have a bandwidth of 5MHz. The antenna percentage bandwidth requirement for 4 simultaneouschannels can be a ratio of 4*5 MHz/2.4 GHz.

In another example, the ranging system can provide translated frequencyband usage. In an example, the beacon and user transceiver nodes canwork at various frequency bands for convenience, which can be translatedfrom ZigBee designated frequencies, or directly derived from the ZigBeedesignated frequencies. Then, the beacon and user transceiver nodes canuse a same ZigBee protocol or modification for ranging.

FIG. 18 illustrates a diagram for reducing scanning time by reducing anumber of messages or by reducing a dwell time in a handshaking protocolvia messaging including received signal strength indicator (RSSI) orreceived signal strength (RSS) information. The handshaking protocol canbe implemented using the ZigBee protocol.

Without a hand shaking modification, a controller (in a control station)can send an inquiry message (e.g., interrogation message) to the usernode and the controller can expect a protocol acknowledge (ACK) signalin return. The acknowledge signal (e.g., an inquiry acknowledge signal)can be separate from the reply message (or other message) sent by theuser node. If the controller does not receive the inquiry acknowledgesignal from the user node, the controller can resend the inquiry messagea specified number of times (e.g., up to three times with time outbetween). If the controller does not receive the inquiry acknowledgesignal or the reply message, the controller can proceeds to next a nextuser node or the controller can wait indefinitely for a reply to bereceived.

If the user node receives the inquiry message, the user node can read ormeasure the RSSI of the inquiry message signal from a receiver registerand the user node can return the RSSI value (along with otherinformation) to the controller in the reply message. If the user nodedoes not receive the reply acknowledge signal, the user node can resendthe reply message a specified number of times (e.g., up to three times).The controller can return the reply acknowledge signal when thecontroller receives the reply message, and the user node may take nofurther action until the next inquiry.

In a modified hand shaking protocol example with a RSSI above threshold,a controller can send an inquiry message 460 (e.g., interrogationmessage) to the user node and the controller can expect a protocolacknowledge (ACK) signal 462 in return. The inquiry message can includea minimum RSSI value. The user node can send a reply message 470 with ameasured RSSI of the inquiry message when the measured RSSI of theinquiry message is greater than or equal to the minimum RSSI value.

Under weak signal conditions, the controller can successfully send theinquiry message to the user node, but the user node signal can be tooweak for the controller to receive the return message after theacknowledge signal. Without a handshaking modification, the controllermay wait indefinitely or for an excessive length of time for a replymessage to be received, which can delay a scan. The controller candetermine a minimum value of RSSI to which the user node can respond.The minimum RSSI value can be contained in the inquiry message packet.If the user node receiver RSSI value is less than the response minimumin the message, the user node sends an acknowledge signal, but may notsend a response message. When the controller receives the acknowledgesignal the controller may not resend the inquiry message.

The acknowledge signal 462 (e.g., an inquiry acknowledge signal) can beseparate from the reply message 470 (or other message) sent by the usernode. If the controller does not receive the inquiry acknowledge signalfrom the user node, the controller can resend the inquiry message aspecified number of times (e.g., up to three times with time outbetween). If the controller does not receive the inquiry acknowledgesignal or the reply message, the controller can proceed to a nextsegment or a next user node after a specified dwell time or time outinterval.

If the user node receives the inquiry message 460, the user node canread or measure the RSSI of the inquiry message signal from a receiverregister and the user node can return the RSSI value (along with otherinformation) to the controller in the reply message 470. If the usernode does not receive the reply acknowledge signal 472, the user nodecan resend the reply message a specified number of times (e.g., up tothree times). The controller can return the reply acknowledge signalwhen the controller receives the reply message, and the user node maytake no further action until the next inquiry.

In another example with a RSSI below threshold (e.g., an RSSI that istoo low), a controller can send an inquiry message 464 (e.g.,interrogation message) to the user node and the controller can expect aprotocol acknowledge (ACK) signal 466 in return. The inquiry message caninclude a minimum RSSI value. The user node can send a acknowledgesignal but not a reply message when the RSSI of the inquiry message isthan the minimum RSSI value. Limiting the transmission of the replymessage by the user node when the RSSI value is too low can conserve thepower resources of the user node.

FIG. 19 illustrates a flow chart for reducing scanning time by reducinga number of messages or by reducing a dwell time in a handshakingprotocol via messaging including received signal strength indicator(RSSI) or received signal strength (RSS) information. The handshakingprotocol can be implemented using the ZigBee protocol.

A control station 120 or controller in the control station can initiatea scan 400 of an end user node 130 via a beacon 110. The scan can startat a first segment in an arc or a raster pattern. The control stationcan set a minimum RSSI (or RSS) for the user node to reply 402. In anexample, the minimum RSSI can change for each segment or arc of a scan.The control station can also set a dwell timer 404, which can specify amaximum length of time a controller will wait for a reply message 420.In an example, the dwell timer can allow for multiple transmissions ofinquiry messages 406, acknowledgements (inquiry acknowledge 410 andreply acknowledge 424 signals), and reply messages 420 plus processingtime and a guard band time.

The control station 120 can send an inquiry message with the minimumRSSI 406 to the end user node. The end user node can read the RSSI ofthe received inquiry message signal from a receiver register or measurethe RSSI of the received inquiry message. The end user node can send aninquiry acknowledge signal 410 back to the control station. The end usernode can determine if the inquiry message RSSI is above the minimum RSSI418 for the end user node to reply. If the inquiry message RSSI is notabove the minimum RSSI, the end user node can wait for an inquirymessage for a next segment interrogation. If the inquiry message RSSI isabove the minimum RSSI, the end user node can send a reply message withthe RSSI information 420 of the inquiry message.

At the control station 120, the control station can wait for the inquiryacknowledge signal 410 from the end user node 130. The control stationcan determine if the inquiry acknowledge signal is received 412. If theinquiry acknowledge signal is not received, the control station candecrement an inquiry timeout counter 414, where the inquiry timeoutcounter counts a specified number of times (e.g., two times) to resendthe inquiry message. The control station can determine if the number ofresent inquiry messages has been reached (e.g., timeout 416). If thecontrol station has not resent the inquiry message a maximum number oftimes, the control station resends the inquiry message. If the controlstation has resent the inquiry message a maximum number of times, thecontrol station can wait for the reply message. If theinquiry-acknowledge signal is received, the control station can wait forthe reply message.

At the end user node 130, the end user node can wait for the replyacknowledge signal 424 from the end user node 130 when a reply messageis sent. The control station can determine if the reply acknowledgesignal is received 426. If the reply acknowledge signal is not received,the user node can decrement an reply timeout counter 428, where thereply timeout counter counts a specified number of times (e.g., twotimes) to resend the reply message. The end user node can determine ifthe number of resent reply messages has been reached (e.g., timeout430). If the end user node has not resent the reply message a maximumnumber of times, the end user node resends the reply message. If the enduser node has resent the reply message a maximum number of times, theend user node can wait for an inquiry message for a next segmentinterrogation.

The control station 120 can determine if the reply message is received422 from the end user node. If the reply message is received, thecontrol station can send a reply acknowledge signal 424 to the end usenode, and the control station can read the RSSI of the received replymessage signal from a receiver register (or measure the RSSI of thereceived reply message 432). The control station can record a read RSSIfor the segment (or record a measured RSSI for the segment 434). Therecorded RSSI can include a RSSI from the inquiry message, a RSSI fromthe reply message, a RSSI from a strongest RSSI of the inquiry messageor the reply message, or a function (e.g., an average) of the RSSI ofthe inquiry message or the reply message. The control station candetermine if the scan is finished 440.

If the reply message is not received, the control station 120 can waitfor the reply message until the segment dwell timer expires 436. If thereply message is not received before the segment dwell timer expires,the control station can record a minimum RSSI for the segment 438 (orother value or indication that a valid RSSI was not received). Thecontrol station can determine if the scan is finished 440. If the scanis not finished, the control station can increment to a next segment 442and repeat the inquiry message interrogation. If the scan is finished,the control station can select the segment (representing an angle of theend user) with the strongest RSSI 444 a. If multiple angles have astrongest RSSI, a midpoint between the multiple angles (e.g., segments)can be used for the angle of the end user node. In another example, thecontrol station can determine a finer resolution of the angle (e.g.,AoA) of the end user node, thereby improving accuracy, by using twoadjacent segments with a strongest RSSI 444 b, as will be described ingreater detail below. A scan can be repeated for a next time segment.

Using two adjacent segments with a strongest RSSI can be used generate afiner AoA resolution, thereby improving accuracy. A finer resolution ofthe RSSI value can assist in the fine resolution of the AoA, therebyimproving accuracy. Using two adjacent segments can improve beacon angleof arrival (AoA) estimates compared to the RSSI approach that selects asingle angle for the antenna beam pointed at the remote user (e.g., enduser node). The method can measure the amplitude from the receivedremote user signal in two adjacent beacon beams, where RSSI quantizationcan be used and smaller quantization values can improve accuracy. Theratio of amplitudes from the two beams can results in an improvedestimate of the angle of arrival rather than only estimating the beam ofarrival. Beams can include every other beam rather than adjacent as longas the two beams used are less than one beamwidth apart.

The following shows the derivation and quantifies the performance ofusing two beacon beams. AoA estimation can be based on amplitude fromtwo similar (or near identical) beams, where the signal of the signal issimilar but in slightly different direction. N1 and N2 can representthermal noises in beacon beam 1 and beam 2, where beam 1 and beam 2 hasa less than or equal to one beamwidth distance orientation from eachother. Θ (e.g., Θ) denotes beacon AoA, and Θ1 and Θ2 denote beampointing of beam 1 and beam 2. The derivation assumes a relativelystationary user, but the derivation can be adapted if the rate ofmovement is known or can be predicted. The thermal noise N1 and N2 canbe assumed to have the same magnitude (i.e., <N1>=<N2>). S1=S*P1(Θ) andS2=S*P2(Θ) are the receiver user signal in the two beams, where S1represent the signal of beam 1, S2 represents the signal of beam 2, Srepresents the generated signal, P1 represents the power of the signalof beam 1, and P2 represents the power of the signal of beam 2. Thesignal power can be represented in term of a signal-to-noise ratio(SNR).

P(Θ|Θ1)=S*Pat(Θ|Θ1)+N1=S*Pat(Θ|Θ1)+S*Pat(Θ|Θ1)/SNR1

P(Θ|Θ2)=S*Pat(Θ|Θ2)+N2=S*Pat(Θ|Θ2)+S*Pat(Θ|Θ2)/SNR2

R=P(Θ|Θ1)/P(Θ|Θ2) can be the measured received power ratio. DEL=10log(P(Θ|Θ1))−10 log(P(Θ|Θ2)) is the measured received power ratio in dB.In vector calculus, DEL is a vector differential operator, usuallyrepresented by the nabla symbol ∇. When applied to a function defined ona one-dimensional domain, it denotes its standard derivative as definedin calculus. When applied to a field (a function defined on amulti-dimensional domain), DEL may denote the gradient (locally steepestslope) of a scalar field, the divergence of a vector field, or the curl(rotation) of a vector field, depending on the way it is applied.

The noise and reference SNR can be set by the beam pointed at user (i e,link budget). P(0)=10 log(S+N)=10 log(S(1+N/S))=10 log(S)+10log(1+1/SNR) for a beam pointed directly at the user.

10 log(1+x)=4.3 ln(1+x)˜4.3x

P(0)˜10 log(S)+4.3/SNR; SNR is analog, not dB and valid for large SNR(>10 dB). Similar beams (or near identical beams) are assumed in thefollowing for ease in derivation. Non-identical beacon beams may use alookup table for each beam or a more complex description depending onthe AoA accuracy desired.

The derivation can be similar for near identical beams (e.g., theprinciple can be the same as near identical beams). In dB space, beamloss, L1=3(Θ−Θ1)̂2/(BW/2)̂2 dB can use the Gaussian beam approximation,where BW is beamwidth. A more complex beam description may be employedto improve accuracy when needed. Beams can be near identical except fora pointing direction (e.g., Θ1 and Θ2) for ease in derivation. 1/SNR1and 1/SNR2 can be independent random variables from Gaussian process,where SNR1 is a SNR for beam 1 and SNR2 is a SNR for beam 2, and N/Srepresent the noise over the signal.

1/SNR1=N/S and <1/SNR1>=<1/SNR2>

DEL(Θ|Θ1,Θ2)=P(Θ−Θ1|Θ1)−P(Θ−Θ2|Θ2) is the measured user signal in dBfrom parabolic approximation.

DEL(Θ|Θ1,Θ2)=3*(Θ−Θ1)̂2/(BW/2)̂2−3*(Θ−Θ2)̂2/(BW/2)̂2+4.3/SNR1−4.3/SNR2

DEL(Θ|Θ1,Θ2)=(−6*Θ1*Θ+3*Θ1̂2+6*Θ*Θ2−3*Θ2̂2)/(BW/2)̂2+4.3/SNR1−4.3/SNR2

The AoA estimate can be represented by Θ.

Θ=[(DEL−4.3/SNR1+4.3/SNR2)(BW/2)̂2+3*Θ2̂2−3*Θ1̂2]/(6*Θ2−6*Θ1)

Θ=[(DEL−4.3/SNR1+4.3/SNR2)(BW/2)̂2]/(6*ΔΘ12)+3*(Θ2+Θ1)/6 whereΔΘ12=Θ2−Θ1, the difference in beam pointing angles.

The expected AoA estimate can eliminate some terms, such as<1/SNR>=<N/S>=<N>/S and <−4.3/SNR1+4.3/SNR2>=0

The resulting AoA can be an unbiased estimate.

Expected AoA estimate can be represented by<Θ>=[DEL(BW/2)̂2]/(6ΔΘ12)+(Θ2+Θ1)/2

<Θ̂2−<Θ> 2>=Var of Θ which can be proportional to 4th moment of Gaussianfield=3σ̂4→3N̂2.

<Θ̂2−<Θ>̂2>=[2*4.3*(BW/2)̂2/(6ΔΘ12)/S]̂2*3N̂2

The AoA estimate standard deviation can be represented byΔΘ=sqt(3)*8.6*(BW/2)̂2/(6ΔΘ12)]/SNR.

σΘ=0.62*BŴ2/(SNRΔΘ12), where SNR is analog.

The AoA error can be represented by σΘ/BW=0.62/(SNR*ΔΘ12/BW) where SNRis analog and σΘ is the standard deviation of the AoA. AoA error isgiven in terms of beacon beamwidth. FIGS. 20 and 21 illustrate graphs ofAoA error relative to beam pair separation, where the error is limitedto <1 beam width separation due to sidelobe ambiguities.

Another example provides a method 500 for communicating between an enduser node and a control station controller used in determining alocation of the end user node relative to a beacon, as shown in the flowchart in FIG. 22. The method includes the operation of transmitting aninquiry message from the controller to the end user node with minimumreceived signal strength indicator (RSSI) message, wherein the minimumRSSI message includes a RSSI threshold for transmitting a reply messagefrom the end user node, as in block 510. The operation of receiving areply message at the controller from the end user node including ameasured RSSI of the inquiry message at the end user node when themeasured RSSI of the inquiry message exceeds the RSSI threshold follows,as in block 520.

Another example provides a method 600 for determining a location of anend user node relative to the at least one beacon, as shown in the flowchart in FIG. 23. The method includes the operation of scanning each ofa plurality of segments in an arc with a separate narrow radio frequency(RF) beam transmitted from the at least one beacon, wherein the arc isin a direction of the end user node, as in block 610. The operation ofreceiving at the beacon a response signal from the end user node basedon a received narrow RF beam at the end user node follows, as in block620. The next operation of the method can be determining at least one ofan angle-of-arrival (AOA) and a time-of-flight (TOF) of the responsesignal, as in block 630. The method can further include calculating anend user node location relative at least one beacon location using atleast one of the AOA and TOF of the response signal, as in block 640.

Various techniques, or certain aspects or portions thereof, may take theform of program code (i.e., instructions) embodied in tangible media,such as floppy diskettes, CD-ROMs, hard drives, non-transitory computerreadable storage medium, or any other machine-readable storage mediumwherein, when the program code is loaded into and executed by a machine,such as a computer, the machine becomes an apparatus for practicing thevarious techniques. In the case of program code execution onprogrammable computers, the computing device may include a processor, astorage medium readable by the processor (including volatile andnon-volatile memory and/or storage elements), at least one input device,and at least one output device. The volatile and non-volatile memoryand/or storage elements may be a RAM, EPROM, flash drive, optical drive,magnetic hard drive, or other medium for storing electronic data. Thebase station and mobile station may also include a transceiver module, acounter module, a processing module, and/or a clock module or timermodule. One or more programs that may implement or utilize the varioustechniques described herein may use an application programming interface(API), reusable controls, and the like. Such programs may be implementedin a high level procedural or object oriented programming language tocommunicate with a computer system. However, the program(s) may beimplemented in assembly or machine language, if desired. In any case,the language may be a compiled or interpreted language, and combinedwith hardware implementations.

It should be understood that many of the functional units described inthis specification have been labeled as modules, in order to moreparticularly emphasize their implementation independence. For example, amodule may be implemented as a hardware circuit comprising custom VLSIcircuits or gate arrays, off-the-shelf semiconductors such as logicchips, transistors, or other discrete components. A module may also beimplemented in programmable hardware devices such as field programmablegate arrays, programmable array logic, programmable logic devices or thelike.

Modules may also be implemented in software for execution by varioustypes of processors. An identified module of executable code may, forinstance, comprise one or more physical or logical blocks of computerinstructions, which may, for instance, be organized as an object,procedure, or function. Nevertheless, the executables of an identifiedmodule need not be physically located together, but may comprisedisparate instructions stored in different locations which, when joinedlogically together, comprise the module and achieve the stated purposefor the module.

Indeed, a module of executable code may be a single instruction, or manyinstructions, and may even be distributed over several different codesegments, among different programs, and across several memory devices.Similarly, operational data may be identified and illustrated hereinwithin modules, and may be embodied in any suitable form and organizedwithin any suitable type of data structure. The operational data may becollected as a single data set, or may be distributed over differentlocations including over different storage devices, and may exist, atleast partially, merely as electronic signals on a system or network.The modules may be passive or active, including agents operable toperform desired functions.

Reference throughout this specification to “an example” means that aparticular feature, structure, or characteristic described in connectionwith the example is included in at least one embodiment of the presentinvention. Thus, appearances of the phrases “in an example” in variousplaces throughout this specification are not necessarily all referringto the same embodiment.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary. In addition, various embodiments and example of the presentinvention may be referred to herein along with alternatives for thevarious components thereof. It is understood that such embodiments,examples, and alternatives are not to be construed as defactoequivalents of one another, but are to be considered as separate andautonomous representations of the present invention.

Furthermore, the described features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments. In thefollowing description, numerous specific details are provided, such asexamples of layouts, distances, network examples, etc., to provide athorough understanding of embodiments of the invention. One skilled inthe relevant art will recognize, however, that the invention can bepracticed without one or more of the specific details, or with othermethods, components, layouts, etc. In other instances, well-knownstructures, materials, or operations are not shown or described indetail to avoid obscuring aspects of the invention.

While the forgoing examples are illustrative of the principles of thepresent invention in one or more particular applications, it will beapparent to those of ordinary skill in the art that numerousmodifications in form, usage and details of implementation can be madewithout the exercise of inventive faculty, and without departing fromthe principles and concepts of the invention. Accordingly, it is notintended that the invention be limited, except as by the claims setforth below.

What is claimed is:
 1. A beacon for a ranging system, comprising: anelectronic scanned array (ESA) antenna configured to emit a separateradio frequency (RF) phased-array narrow beam for each of a plurality ofsegments of an arc, and configured to receive from an end user node aresponse signal based on at least one of the RF phased-array narrowbeam, wherein each segment of the arc is scanned at a specified timeinterval; and a transceiver configured to transmit a pulsed signal viathe RF phased-array narrow beam, and receive the response signal.
 2. Thebeacon of claim 1, further comprising: a processing module configured tocalculate at least one of an angle-of-arrival (AOA) and a time-of-flight(TOF) from the response signal and generate a location of the end usernode relative to a location of the beacon.
 3. The beacon of claim 2,wherein the processing module is further configured to determine anabsolute location of the end user node by information selected from thegroup consisting of GPS coordinates, horizontal level adjustments,rotational face direction of the ESA antenna, angle adjustment of theESA antenna, and combinations thereof.
 4. The beacon of claim 2, whereinthe processing module is further configured to measure a received signalstrength indicator (RSSI) from the received response signal.
 5. Thebeacon of claim 1, further comprising: a node networking antennaconfigured to communicate with other beacons and a control module via alocal area network (LAN).
 6. The beacon of claim 1, further comprising anode networking antenna configured to communicate with at least one enduser node upon interrogation, wherein the at least one end user nodeprovides at least one of navigation information, biometric information,an acknowledgement signal, and end user node status information via thenode networking antenna.
 7. The beacon of claim 1, The beacon of claim1, wherein the ESA antenna includes components selected from the groupconsisting of a beam controller, a plurality of radiator apertures, aphase shifter, a splitter or a summer, and combinations thereof.
 8. Thebeacon of claim 7, wherein the ESA antenna includes a plurality ofradiator apertures configured in at least an array of a row or a column.9. The beacon of claim 1, wherein the ESA antenna includes a right handcircularly polarized (RHCP) antenna or a left hand circularly polarized(LHCP) for reducing multi-path reflections.
 10. The beacon of claim 1,wherein the beacon uses a modified Institute of Electrical andElectronics Engineers (IEEE) 802.15.4 standard or modified ZigBeeprotocol for signal transmissions, wherein the modified IEEE 802.15.4 ormodified ZigBee protocol reduces scanning time by reducing a number ofmessages or by reducing a dwell time in a handshaking protocol viamessaging including received signal strength indicator (RSSI)information.
 11. A method for communicating between an end user node anda control station controller used in determining a location of the enduser node relative to a beacon, comprising: transmitting an inquirymessage from the controller to the end user node with minimum receivedsignal strength indicator (RSSI) message, wherein the minimum RSSImessage includes a RSSI threshold for transmitting a reply message fromthe end user node; and receiving a reply message at the controller fromthe end user node including a measured RSSI of the inquiry message atthe end user node when the measured RSSI of the inquiry message exceedsthe RSSI threshold.
 12. The method of claim 11, further comprising:incrementing to a next segment in a plurality of segments of a scanafter a maximum segment time, wherein each segment of the plurality ofsegments uses a different radio frequency (RF) phased-array narrow beamfor transmitting an inquiry message and receiving the reply message, andthe maximum segment time provides a specified dwell time interval fortransmitting the inquiry message and receiving the reply message; andtransmitting the inquiry message and receiving the reply message for thenext segment.
 13. The method of claim 11, further comprising afterreceiving the reply message: measuring the RSSI of the reply message;and determining at least one of an angle-of-arrival (AOA) and atime-of-flight (TOF) of the reply message or the inquiry message fedback in the reply message.
 14. The method of claim 13, furthercomprising after receiving the reply message: determining at least oneof an AOA and a TOF of the end user node relative to the beacon from agreatest RSSI strength of a plurality of reply messages, wherein atleast one of a RSSI of the reply message and a RSSI of inquiry messagefed back in the reply messages has a greatest RSSI strength relative toother reply messages or inquiry messages.
 15. The method of claim 13,further comprising after receiving the reply message: determining ashortest TOF between the end user node and the beacon from a pluralityof reply messages, wherein the shortest TOF is at least one of a TOF ofthe reply messages and a TOF of the inquiry messages relative to otherreply messages or inquiry messages.
 16. The method of claim 11, whereintransmitting the inquiry message and receiving the reply message uses aradio frequency (RF) phased-array narrow beam via an electronic scannedarray (ESA) antenna of a beacon.
 17. The method of claim 11, whereincommunicating between the end user node and the control stationcontroller uses a modified Institute of Electrical and ElectronicsEngineers (IEEE) 802.15.4 standard or modified ZigBee protocol forsignal transmissions, wherein the modified IEEE 802.15.4 or modifiedZigBee protocol reduces scanning time by reducing a number of messagesor by reducing a dwell time in a handshaking protocol via messagingincluding received signal strength indicator (RSSI) information.
 18. Atleast one non-transitory machine readable storage medium comprising aplurality of instructions adapted to be executed to implement the methodaccording to claim
 11. 19. An end user node for a ranging system,comprising: a receiving module configured to receive an inquiry messagefrom a controller with minimum received signal strength indicator (RSSI)message, wherein the minimum RSSI message includes a RSSI threshold fortransmitting a reply message; a measurement module configured to measurea RSSI of the inquiry message; and a transmitting module configured totransmit a reply message to the controller including the measured RSSIof the inquiry message at the end user node when the measured RSSI ofthe inquiry message exceeds the RSSI threshold.
 20. The end user node ofclaim 19, wherein the end user node uses an Institute of Electrical andElectronics Engineers (IEEE) 802.15.4 standard or a ZigBee protocol forsignal transmissions.